A mammogram can find breast cancer before a lump can be felt. A mammogram is the best method available today to detect breast cancer early. Early detection of the disease may allow more treatment options.
What Are the Limitations*of Getting Mammograms?
Mammograms may miss cancer that is present. Mammograms may find something that turns out NOT to be cancer.
*These limitations occur more often in women under age 50.
Oral Contraceptives and Cancer Risk
Oral contraceptives (OCs) first became available to American women in the early 1960s. The convenience, effectiveness, and reversibility of action of birth control pills (popularly known as "the pill") have made them the most popular form of birth control in the United States. However, a correlation between estrogen and increased risk of breast cancer has led to continuing controversy about a possible link between OCs and cancer.
This fact sheet addresses only what is known about OC use and the risk of developing cancer. It does not deal with the most serious side effect of OC use-the increased risk of cardiovascular disease for certain groups of women.
Oral Contraceptives
Currently, two types of OCs are available in the United States. The most commonly prescribed OC contains two synthetic versions of natural female hormones (estrogen and progesterone) that are similar to the hormones the ovaries normally produce. Estrogen stimulates the growth and development of the uterus at puberty, thickens the endometrium (the inner lining of the uterus) during the first half of the menstrual cycle, and stimulates changes in breast tissue at puberty and childbirth. The two types of synthetic estrogens used in OCs are ethinyl estradiol and mestranol.
Progesterone, which is produced during the last half of the menstrual cycle, prepares the endometrium to receive the egg. If the egg is fertilized, progesterone secretion continues, preventing release of additional eggs from the ovaries. For this reason, progesterone is called the "pregnancy-supporting" hormone, and scientists believe it to have valuable contraceptive effects. The synthetic progesterone used in OCs is called progestogen or progestin. Norethindrone and levonorgestrel are examples of synthetic progesterones used in OCs.
The second type of OC available in the United States is called the minipill and contains only a progestogen. The minipill is less effective in preventing pregnancy than the combination pill, so it is prescribed less often.
Because medical research suggests that cancers of the female reproductive organs sometimes depend on naturally occurring sex hormones for their development and growth, scientists have been investigating a possible link between OC use and cancer risk. Medical researchers have focused a great deal of attention on OC users over the past 30 years. This scrutiny has produced a wealth of data on OC use and the development of certain cancers, although results of these studies have not always been consistent.
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Breast Cancer
A woman's risk of developing breast cancer depends on several factors, some of which are related to her natural hormones. Hormonal factors that increase the risk of breast cancer include conditions that allow high levels of estrogen to persist for long periods of time, such as early age at first menstruation (before age 12), late age at menopause (after age 55), having children after age 30, and not having children at all. A woman's risk of breast cancer increases with the amount of time she is exposed to estrogen.
Because many of the risk factors for breast cancer are related to natural hormones, and because OCs work by manipulating these hormones, there has been some concern about the possible effects of medicines such as OCs on breast cancer risk, especially if women take them for many years. Sufficient time has elapsed since the introduction of OCs to allow investigators to study large numbers of women who took birth control pills for many years, beginning at a young age, and to follow them as they became older.
Studies examining the use of OCs as a risk factor for breast cancer have produced inconsistent results. Scientists suggest the inconsistent findings may have occurred because participants in different studies used OC in different doses and forms. In addition, other factors that influence baseline hormone levels in the women under study may have led to different results among the studies. In general, most studies have not found an overall increased risk for breast cancer associated with OC use. In June 1995, however, investigators at the National Cancer Institute (NCI) reported an increased risk of developing breast cancer among women under age 35 who had used birth control pills for at least 6 months, compared with those who had never used OCs. They also saw a slightly lower, but still elevated, risk among women ages 35 to 44. In addition, their research showed a higher risk among long-term OC users, especially those who had started taking the pill before age 18.
A 1996 analysis of worldwide epidemiologic data, which included information from the 1995 study, found that women who were current or recent users of birth control pills had a slightly elevated risk of developing breast cancer. However, 10 years or more after they stopped using OCs, their risk of developing breast cancer returned to the same level as if they had never used birth control pills.
To conduct this analysis, the researchers examined the results of 54 studies conducted in 25 countries that involved 53,297 women with breast cancer and 100,239 women without breast cancer. More than 200 researchers participated in this combined exhaustive analysis of their original studies, which represented about 90 percent of the epidemiological studies throughout the world that had investigated the possible relationship between OCs and breast cancer.
The return of risk to normal levels after 10 years or more of not taking OCs was consistent regardless of family history of breast cancer, reproductive history, geographic area of residence, ethnic background, differences in study designs, dose and type of hormone, and duration of use. The change in risk also generally held true for age at first use; however, for reasons that were not fully understood, there was a continued elevated risk among women who had started to use OCs before age 20.
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Scientists suggest that the slightly elevated risk seen in both current OC users and those who had stopped use less than 10 years previously may not be due to the contraceptive itself. The slightly elevated risk may result from the potential of estrogen to promote the growth of breast cancer cells that are already present, rather than its potential to initiate changes in normal cells leading to the development of cancer.
Furthermore, the observation that the slightly elevated risk of developing breast cancer that was seen in this study peaked during use, declined gradually after OC use had stopped, then returned to normal risk levels 10 years or more after stopping, is not consistent with the usual process of carcinogenesis (the process by which normal cells are transformed into cancer cells). It is more typical for cancer risk to peak decades after exposure, not immediately afterward. Cancer usually is more likely to occur with increased duration and/or degree of exposure to a carcinogen (cancer-causing substance). In this analytical study, neither the dose and type of hormone nor the duration of use affected the risk of developing breast cancer.
